gdbserver: redo stepping over breakpoint that was on top of a permanent breakpoint

gdbserver: redo stepping over breakpoint that was on top of a permanent breakpoint

I'm going to add an alternate mechanism of breakpoint trap
identification to 'check_stopped_by_breakpoint' that does not rely on
checking the instruction at PC.  The mechanism currently used to tell
whether we're stepping over a permanent breakpoint doesn't fit in that
new method.  This patch redoes the whole logic in a different way that
works with both old and new methods, in essence moving the "stepped
permanent breakpoint" detection "one level up".  It makes lower level
check_stopped_by_breakpoint always the adjust the PC, and then has
linux_wait_1 advance the PC past the breakpoint if necessary.  This
ends up being better also because this now handles
non-decr_pc_after_break targets too.  Before, such targets would get
stuck forever reexecuting the breakpoint instruction.

Tested on x86_64 Fedora 20.

gdb/gdbserver/ChangeLog:
2015-02-23  Pedro Alves  <palves@redhat.com>

	* linux-low.c (check_stopped_by_breakpoint): Don't check if the
	thread was doing a step-over; always adjust the PC if
	we stepped over a permanent breakpoint.
	(linux_wait_1): If we stepped over breakpoint that was on top of a
	permanent breakpoint, manually advance the PC past it.